Abstract <p>Two-dimensional (2D) materials, due to their atomically thin structure, are highly susceptible to environmental degradation such as oxidation and moisture absorption. These effects can significantly reduce performance and stability, making surface passivation a critical requirement for practical applications. In this work, we investigate the effects of high-k hafnium dioxide (HfO₂) dielectric deposited by atomic layer deposition on transition metal dichalcogenides (TMDs), including MoTe₂, MoS₂, and WSe₂. To enable uniform dielectric growth and interfacial bonding, oxygen plasma pre-treatments are applied to form reactive sites prior to deposition. Atomic force microscopy confirmed that the surface roughness of HfO₂ decreases with longer plasma treatment, indicating improved nucleation and conformal coverage on the TMDs surface. Electrical measurements of back-gated field-effect transistors demonstrate a clear dependence of doping behavior on HfO₂ thickness. In thicker films, electrons supplied from oxygen vacancies within HfO₂ to the TMDs channel increases. Additionally, electrons are further induced into the channel by the positive fixed charge, resulting in strong n-type doping effects for thicker HfO₂ layers, as evidenced by the enhanced n-type on-state current. In contrast, devices with thinner HfO₂ films exhibit weaker n-type doping effect or even p-type behavior, likely due to the dominant influence of plasma-induced surface modifications. These results indicate the importance of optimizing both plasma treatment conditions and dielectric thickness to achieve desirable doping and passivation effects. Overall, this study presents a viable strategy for controlled the integration of high-k dielectrics with 2D semiconductors, contributing to the advancement of stable, scalable, and high-performance 2D electronic devices.</p> Graphical Abstract <p></p>